Continuous method of manufacturing articles from foamed thermoplastic material

ABSTRACT

An integrated method of continuously extruding low-density foamed thermoplastic material and manufacturing threedimensionally formed articles therefrom. The method includes the steps of extruding and spreading a narrow strip of thermoplastic material at a high linear rate, vacuum forming articles therefrom on the periphery of a forming wheel (utilizing the heat of extrusion), severing the formed articles from the strip, packaging the articles, and returning the selvage for re-use.

United States Patent Winstead *Jan. 29, 1974 [54] CONTINUOUS METHOD OF3,676,537 7/1972 Winstead 264/48 MANUFACTURING ARTICLES FROM 3,238,5653/1966 Jacobs 264/321 X 3,311,681 3/1967 Chemey et al. 264/48 FOAMEDTHERMOPLASTIC MATERIAL 2,902,718 9/ 1959 Martelli et a1. 264/90 [76]Inventor: Thomas W. Winstead, 2 Overlook 3,389,203 6/1968 Merges et a1.264/37 L B lti Md 21210 3,391,051 7/1968 Ehrenfreund et a1 264/48 X3,426,111 2/1969 Simpson 264/48 l Nome: The portion of the term of thls3,317,363 5/1967 Weber 264/321 x patent subsequent to June 13, 1989, hbeen i 1 i FOREIGN PATENTS OR APPLICATIONS Filed Jan 15 1971 291,9407/1965 Netherlands 264/51 PP N04 106,861 Primary Examiner-Phi1ip E.Anderson Related s Application Data Attorney, Agent, or Firm-RaphaelSemmes [60] Continuation-impart of Ser. No. 798,821, Oct. 10,

1968, abandoned, which is a division of Ser. No. [57] ABSTRACT 480,917,Aug. 19, 1965, Pat. No. 3,479,694.

An integrated method of continuously extruding low- 52 us Cl 264/51,264/53, 264/210 R, density foamed thermoplastic material and manufac- 77264/32] 264N310 5 turing three-dimensionally formed articles therefrom.264/D1G. 13, 264/D1G. 16,425/4 C,425/224 The method includes the stepsof extruding and 5 Int. Cl 329d 7 m 329d 7 /24, 329d 27/00 spreading anarrow strip of thermoplastic material at a 5 Field f Search 425/4 C;425/224; 2 4/4 51 high linear rate, vacuum forming articles therefrom On264/53, 321, 90 37 the periphery of a forming wheel (utilizing the heatof extrusion), severing the formed articles from the strip, 5 ReferencesCited packaging the articles, and returning the selvage for UNITEDSTATES PATENTS 3,670,059 6/1972 Winstead 264/48 12 Claims, 20 DrawingFigures TIIII'. will mmwmm 3.789.095

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sum 13m 13 I33 1 I 1 I l I I I I I I I I l I I I I E '4 Ln! g WH q- 0 1L1 X 7 Q o 0 k N N xx m- N t 8 g\ o INVENTOR THOMAS W. WINSTEAD BY umATTORNEY CONTINUOUS METHOD OF MANUFACTURING ARTICLES FROM FOAMEDTHERMOPLASTIC MATERIAL REFERENCE TO CO-PENDING APPLICATIONS Thisapplication is a continuation-in-part of Ser. No. 798,821, filed Oct.10, 1968, and now abandoned which is a division of Ser. No. 480,917,filed Aug. 19, 1965 for Continuous Method and Apparatus forManufacturing Articles from Foamed Thermoplastic Material, now U.S. Pat.No. 3,479,694, granted Nov. 25, 1969. Reference is also made toco'pending application Ser. No. 475,734, filed July 29, 1965, now U.S.Pat. No. 3,387,328, granted June 11, 1968, and to application Ser. No.882,866, filed Dec. 8, 1969, now U.S. Pat. No. 3,676,537 which is acontinuation-in-part of application Ser. No. 508,417, filed Nov. 18,1965 (now abandoned).

BACKGROUND OF THE INVENTION This invention relates to a method ofproducing three-dimensionally formed articles of low-density foamedthermoplastic material on a continuous, integrated basis, and is moreparticularly concerned with the extrusion of the thermoplastic materialand the production and packaging of the articles without interruption.

The present invention is concerned with the production of low-cost,three-dimensionally formed articles of thermoplastic material of lowdensity. Low density as employed herein means a density of up to aboutthree pounds per cubic foot. Three-dimensionally formed articles meansarticles molded individually to a depth of at least of the orderthree-eighths inch in orthogonal planes, e.g., trays or cups.

It has been the usual practice in making formed articles from foamedthermoplastics to employ a multiple stage method and apparatus. First,foamed sheeting is extruded and collected on rolls which are storeduntil ready for use in a sheet-forming machine, which reheats thematerial on a progressive basis and forms it in molds by the use ofdifferential air pressure, plungers, or both. After forming, the web istransferred to a cutting machine which severs the formed articles fromthe selvage. The extrusion operation, the forming operation, and thecutting operation require entirely separate steps and machinery, andalthough this system has been satisfactory in certain respects, it hasmany limitations affecting cost, quality control and operationalcontrol.

For example, with the conventional multiple stage operation, thefollowing disadvantages and limitations are noted:

1. Considerably more floor space is required for the multiple steps andmachinery than is required for an integrated system.

2. Because of the usual blown bubble method used in producing the sheet,it is very difficult to produce low density material of good quality,and this naturally affects cost.

3. Because of the separation of the extrusion and fabricatingoperations, quality control becomes more difficult and costly; aconsiderable amount of sheeting may be made for subsequent forming withdefects which are not detected until the forming operation is begun, atwhich time it is too late to take corrective measures.

This naturally results in the rejection of large quantities of material.

4. Since foam sheeting has excellent thermal insulating properties, itis difficult and costly from an energy standpoint to heat it properlyand uniformly during the fabrication step.

5. With certain types of thermoplastic foam sheeting, there is a periodof aging during which volatiles used in the foaming process are evolvedand replaced by air. Therefore, careful attention must be paid to thetime when the re-heating takes place during the fabricating step,because the residual content of the volatile can have an appreciableeffect on the final density of the product, necessitating operationalcontrols which further complicate the process.

6. Because of the difficulties in obtaining uniform heat and because ofthe necessity of waiting until a large percentage of the volatiles hasevolved from the material, it is not possible to form such foamedsheeting as readily or as deeply as would otherwise be the case.

7. A multiple stage process is always more difficult to automate andnecessarily requires more manpower than an integrated process, whichagain affects costs adversely.

Continuous processes attempted heretofore for manufacturing foamedarticles have not been capable of producing high-quality low-densityarticles economically, especially where vacuum forming is employed.

BRIEF DESCRIPTION OF THE INVENTION It is accordingly a principal objectof the invention to provide an improved method of producing articles offoamed thermoplastic material, particularly threedimensionally formedarticles of low density.

A more specific object of the invention is to provide a unique method ofproducing such articles economically on a continuous basis, in which theextruding, forming, cutting, and packaging operations take place withoutinterruption and without the necessity of reheating the extrudedmaterial before forming, the individual steps of the method beingcoordinated so as to produce articles of high quality.

Briefly stated, in accordance with a preferred embodiment of the presentinvention, thermoplastic material, such as polystyrene resin stock, forexample, heated to an appropriate temperature and mixed with a volatileblowing agent, is extruded so as to produce a flat, narrow-strip,low-density foamed extrudate at a high linear rate. The extrudate isspread laterally over a mandrel, from which it is immediately fed torotating vacuum molding apparatus. The resultant threedimensionallyformed articles are stripped from their molds, severed from the foamweb, stacked, and packaged without interruption, the selvage beingreclaimed. Critical operating parameters permit deep-drawthreedimensional vacuum molding on a continuous basis without requiringreheating of the extrudate, without adversely affecting the density andcell structure of the foam, and without introducing wrinkles or otherimperfections.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be furtherdescribed with reference to the accompanying drawings, which illustratetypical apparatus for performing the process of the invention, andwherein:

FIG. 1 is a schematic view illustrating an integrated system which maybe employed in the method of the invention;

FIG. 1A is a longitudinal sectional view illustrating the extruder headand mandrel;

FIG. 1B is an end view showing the extrusion die and mandrel andillustrating an extruded sheet of foamed thermoplastic passing over themandrel from the die lips;

FIG. 2 is an elevational view partially in section illustrating theforming wheel unit;

FIG. 3 is a plan view partially in section taken at right angles to theillustration in FIG. 2;

FIG. 4 is an enlarged side elevation of the forming wheel;

FIG. 5 is a sectional view taken on line 5-5 of FIG. 4, illustrating themold structure;

FIG. 6 is a further enlarged plan view of a mold;

FIG. 7 is a sectional view taken on line 77 of FIG.

FIG. 8 is a similar view taken on line 8-8 of FIG. 6;

FIG. 9 is a plan view of the vacuum control manifold valve plate;

FIG. 10 is a sectional view taken on line 10--10 of FIG. 9;

FIG. 11 is a sectional view taken on line 1111 of FIG. 9;

FIG. 12 is a top plan view of the article cutting unit;

FIG. 13 is a sectional view taken on line 13-13 of FIG. 12;

FIG. 14 is a sectional view taken on line 14l4 of FIG. 13;

FIG. 15 is a sectional view taken on line 15-15 of FIG. 12;

FIG. 16 is a feeding end elevation of the packaging unit;

FIG. 17 is a view of the same in side elevation; and

FIG. 18 is the delivery end elevation.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1, apreferred integrated system for performing the method of the inventionincludes an extrusion device generally indicated at 20, which ispreferably of the type shown and described in my copending applicationSer. No. 475,734, filed July 29, 1965, now U.S. Pat. No. 3,387,328,granted June 8.- He e a c p n ble thsrm last sma qia incorporatingsuitable blowing agents is extruded through a die, forming a continuousnarrow thermoplastic foam strip or sheet 22. The sheet 22 travels over aspreading yoke or mandrel 23, also shown in said copending ApplicationSer. No. 475,734, now U.S. Pat. No. 3,387,328, from which it isconducted around the periphery of a forming wheel 24 which vacuum formsthe articles on the sheet 22.

By sequential valving, to be described, the vacuum is applied to thesuccessive molds on the forming wheel 24 as the sheet 22 is tangent tothe respective flat faces of the forming wheel and after the sheet hasbeen flattened and stretched by the spreading yoke 23.

The formed articles, while still carried by the sheet 22, are thenstripped tangentially from the upper side of the forming wheel, and thesheet and articles are conducted to the cutting unit 25 where the formedarticles are removed from the sheet and directed to a stacking unit 26.The remaining selvage 22a is thereupon conducted to a granulatingmachine 27 which automatically divides it into fine particles, afterwhich it is fed back into the extrusion equipment. In order tofacilitate the sequential operation of the integrated units .of thesystem and to insure proper spacing of said units,

the forming wheel unit 24, the cutting unit 25 and the stacking unit 26are mounted on suitable wheels or rollers 28, 29 and 30 respectivelywhich may run on tracks, as shown.

The present invention employs low-density material, and as will be seenhereinafter, this requires the production and utilization of anarrow-strip, low-density extrudate at a high linear rate. If highquality articles are to be produced, the low-density extrudate must,first of all, be free of wrinkles and other defects. Such an extrudatecan be produced as set forth in the aforesaid copending application Ser.No. 475,734, now U.S. Pat. No. 3,387,328, but not by conventionalextrusion dies, such as the flat slit die. When foamed plastics areextruded from a die the extrudate immediately expands as it merges fromthe die lip. This expansion is threedimensional and the amount ofexpansion depends fundamentally upon the resulting density. For example,if a resin is extruded which has an original density of 60 lbs. percubic foot and by the addition of cells the density is reduced to 3 lbs.per cubic foot, the extrudate expands about 2.7 times in each dimensionas it emerges from the die. Assuming for the moment that the expansionin thickness of the extrudate is of little concern (since the thicknessdimension of the sheet is relatively small to begin with) and thatlongitudinal expansion is of little concern (since the rate at which theextrudate is taken off can readily be made 2.7 times the take-off speedwhich would prevail if the material were not expanding), there stillremains the problem of the width dimension which increases 2.7 times. Ifthe extrudate is 3 inches wide before expansion from the orifice of aflat slit die, the sheet after expansion is over 8 inches wide. At thecenter line of the die orifice, this is of no particular concern,inasmuch as the center line remains the center line as the materialexpands and is taken off. However, the edge of the extrudate must moverapidly from a point 1 /2 inches from the center line to a point over 4inches from the center line. Since most of the expansion in a cellularmaterial occurs very close to the die orifice, the geometry of suitableapparatus to cope with this width-wise expansion problem is critical. Ifthis expansion is not properly accommodated, the extrudate willcorrugate or wrinkle, particularly with lowdensity foam, resulting inpoor quality or an unusable product. The conventional flat slit diefails to accommodate the width-wise expansion.

In tubular extrusion of foam sheet, the wrinkling or corrugation problemis controlled to some degree by the bubble method. As the tube emergesfrom the circular die orifice, it is expanded by the internally trappedair or by an internal shoe which helps to remove the wrinkles orcorrugations. However, this method has geometric limitations whichpreclude the extrusion and wrinkle-free spreading of low-density foam,and which preclude the collapsing or slitting of the tubular extrudateclose enough to the die and soon enough to permit subsequent formingoperations while the extrudate retains enough heat to be sufficientlypliable.

As set forth in the aforesaid co-pending application Ser. No. 882,866,and in the said co-pending Application Ser. No. 475,734, now US. Pat.No. 3,387,328, and as shown in FIGS. 1A and 1B, a suitable narrowstripextrudate 22 can be produced at a high linear rate by a diverging diechamber which has a cylindrical outlet. A charge of molten thermoplasticraw material is fed under pressure to the central passageway 6 of theextruder body 5. The thermoplastic raw material may be a compositioncomprising polymers of ethylenically unsaturated monomers, such aspolystyrene, polyethylene, polyvinyl chloride, or polypropylene, forexample general purpose styrene containing percent by weight of anon-inflammable volatile liquid blowing agent, such astrichlorofluoromethane (or pentane), and a suitable nucleating agent,such as 1 percent by weight of inorganic talc. The discharge end of thepassageway or barrel 6 passes through an extruder head 7 and preferablyterminates in communication with a converging inlet port 8 locatedcentrally of a circular die plate 9. An end cap 10, also circular inshape, registers with the plate 9, being secured in place by anysuitable means, and the inner face of the end cap is conically recessed,as at 11, providing, with the plate 9, a feed chamber 12 which iscoaxial with the passageway 6 and converging opening 8. The conicalfront wall of the chamber terminates slightly inward of the periphery ofthe end cap 10 and is circumscribed by a narrow annular wall at theperiphery. An adapter 13 conforms substantially to the surface contourof the chamber 12, with the exception that the upper portion thereof isprovided with a V-shaped cut-out area, which, when the adapter isinstalled, provides the upwardly diverging radial confines 120 for thechamber 12a, thereby providing a substantially fan-shaped die reservoir,the upper portion of which terminates in the cylindrical lips 12b (seeFIG. 1B). The outlet opening of the die is. a circular arc in the planeof the flat extrudate, the arclength of the die opening being chosen toproduce a narrow-strip extrudate, which will be considered later indetail. Internally of the die, the material flow begins at a point whichis equidistant from all points on the cylindrical die lips. Thisprovides a uniform distribution of flow pressure at all points along thelips and thereby eliminates strains or distortions in the extrudate.

To ensure the controlled spreading of the extrudate after it leaves thedie lips, a mandrel or spreader 23 is provided adjacent to the die lips.The mandrel preferably comprises a transversely arcuate tube (generallyparallel to the die lips) which is supported in an upright position, sothat as the extrudate leaves the die lips and expands, it moves radiallyoutward to the mandrel, spreading laterally over the mandrel while beingsupported thereby, to provide maximum accommodation of the width-wiseexpansion of the extrudate.

In the space between the cylindrical die orifice and the mandrel, anycorrugations or wrinkles which may tend to form in the expandingcellular strip are very efficiently and quickly removed. The mandrel ispreferably hollow in order to provide for circulating coolant, and itssurface may be coated with an anti-friction surface coating. The fiow ofmaterial over the mandrel not only serves to prevent corrugations orwrinkles which would otherwise form upon expansion of the extrudate, butalso, if proportioned properly and positioned properly, the mandrel canactually provide transverse stretch to the sheet as it is pulledlongitudinally around the mandrel.

As the extruded strip passes over the mandrel, it may be drawn away atan oblique or acute angle with respect to the plane of the mandrel, asshown in FIG. 1. If the mandrel is concentric to the cylindrical dieopening, nothing further is gained by drawing away the extrudate at morethan a degree angle to the plane of the mandrel. However, if thetake-away ah g le is l ess than 90degrees, becoming acute with respectto the plane of the mandrel or more nearly parallel to the mandrelplane, the shape of the mandrel may then be made other than concentricwith the die opening, either by making it elliptical in shape, ratherthan circular, or by moving it closer to the die opening, whicheffectively does the same thing, In practice, the extruded strip may bedrawn away from the mandrel in a direction almost opposite to thedirection of the extrudate flow from the die opening to the mandrel.Although not absolutely essential to the process, the geometry of thedirection of the extrusion (upward) and the reversal (downward) as theextrudate flows to the bottom of the forming wheel is considered quiteadvantageous. This permits maximum employment of the circumference ofthe forming wheel for cooling and setting the formed articles prior totheir tangential stripping from the top of the forming wheel. If othergeometry is used, one if faced with the loss of the greater portion ofthe circumference of the forming wheel for cooling, and/or a removalpoint which would not permit convenient location of the cuttingapparatus and the maintenance of suitable tension between the twomachines.

Although one might suppose that it would be best to extrude a fairlywide sheet, in order to have a web width which accommodates a largenumber of molding cavities, just the opposite is true in the process ofthe invention. If three-dimensional forming is to be carried out byutilization of the heat of extrusion (without reheating of theextrudate), this being essential in accordance with the invention, theextrudate must be produced as a narrow strip which is fed at a high feedrate to the molding apparatus. This is especially so if the articles areto be made by vacuum forming, where the material must have sufficientplasticity to permit deep draws with the low pressure available. As theextrudate emerges from the die, it expands rapidly, because the blowingagent, which previously has been in solution due to pressures in thesystem of perhaps 500 psi or more, is no longer under more thanatmospheric pressure (approximately 15 psi), and at the lower pressurethe blowing agent comes out of solution and volatilizes. This change ofstate naturally absorbs heat energy, thus rapidly lowering thetemperature of the extrudate. The decrease of temperature is especiallypronounced in low-density foam. In wide sheets fed at conventional slowspeeds, the additional heat loss through radiation and convectionbecomes intolerable. A narrow web feb at high speed minimizes heat lossfrom the material and makes feasible the continuous process of theinvention.

A high percentage of volatile blowing agents may be employed inextrudable foams, such as styrene, and such agents have a plasticizingeffect on a polymer. The narrow-strip, high-linear-rate concept of theinvention permits the forming step to take place immediately afterextrusion and to benefit from the plasticizing effect of the volatileblowing agents. Moreover, when a narrow strip is used, as in the presentinvention, corrugations or wrinkles in the web can be overcome, as setforth above, by stretching the material to the greater arc length of themandrel. With wide or tubular lowdensity extrudate, the problem ofavoiding or removing such defects is insurmountable.

The high linear rate of feed is also an important factor in eliminatingthe possibility of crushing of the strip as it passes over the spreaderor mandrel. A wider sheet, and its inherently slower feed rate, wouldmake cell collapse a definite difficulty. However, in the method of theinvention, the extruded material is still expanding as it reaches themandrel, since its temperature is still well above the boiling point ofthe volatile blowing agents, and the cells are under appreciableinternal pressure, making them resilient enough to resist crushing.

With the higher density foam generally employed in the prior art, heatloss due to volatilization is considerably less, and it is possible(although difficult) to re-heat the extrudate. The addition of heat fromoutside of the extrudate, which must pass through the outer portions inorder to reach inner portions, is extremely difficult and impracticalwith low-densityfoam, because of the exceptional thermal insulatingcharacteristics of the foam itself. Since heat transfer is so poor inlow-density foams, time and distance factors become critical.Furthermore, because of the poor heat transfer characteristics oflow-density foam, an uneven temperature profile is developed across theweb thickness during reheating, which results in poor forming or stressin the finished product. Unevenness of temperature profile is aggravatedif an effort is made to decrease time of heating by increasing theintensity of heat, and uniformity is sacrificed.

It might be assumed that stock temperatures coming from the extrusiondie could be increased in order to compensate for the loss of heat.However, with foamed materials there is a limit beyond which the stocktemperature cannot be increased without causing cell collapse and/orbrittleness. For example, with styrene this limit is of the order of300F. in the die chamber. The narrow-strip, high-feed-rate concept ofthe invention is the solution to the problem.

To summarize, the narrow-strip, high-feed-rate concept of the inventionminimizes wrinkles or corrugations in the material as the materialexpands from the die orifice; it minimizes the loss of heat content,which is inherently so rapid in an expanding low-density foam extrudate;it minimizes the loss of volatiles, which have benefical plasticizingeffects; and it maximizes the capability of making low-density,deep-drawn articles of high quality of low cost.

.HJLPELQQQIQWQQ h ein ntt e w h the strip is optimally within the rangeof from less than 1 to a maximum of 18 inches wide after expansion, andthe thickness is optimally between 0.020 and 0.300 inch after expansion.A typical temperature profile beginning with the stock in the die isshown in the follow- Compared to prior art extrusion-forming methods,the feed rate of the extrudate produced by the invention is very high.Assuming a density of 2.5 pounds per cubic foot and a final thickness ofthe extrudate of 0.125 inch, for example, the following linear extrudatefeed rates are typical for the stated widths and pounds per hour ofextrudate produced:

TABLE II l00 lb. per hr. 200 lb. per hr. 300 lb. per hr.

6" width 128 ft. per min. 256 ft. per min. 384 ft. per min. 128 ft. permin. 192 ft. per min.

12" width 64 ft. per min.

The minimum feed rate is of the order of 40 feet per minute. The size ofdisposable and packaging products which are produced by the inventiondictates that for 9 0 percent of all production, extrudate widths willbe from 6 inches to 12 inches. The following table gives typicaloperating conditions:

TABLE Ill In a typical system for carrying out the method of theinvention, the mandrel is located between 2 and 3 inches away from thedie lip, and the near edge of the mold at which forming is commenced isabout 6 inches from the mandrel along the path of the extrudate.

As seen in FIGS. 2 5, the forming wheel 24 comprises a series of fiat,peripherally mounted molds 31, which, in the embodiment illustrated,jointly form a wheel of octagonal periphery. These molds are supportedon a wheel disc 32 by suitable screw-threaded fixtures 33 (FIGS. 4 and5) engaging cross bars 33a, fixed to the outer edge of disc 32. By meansof these fixtures, the individual molds may also be radially adjusted onthe disc for proper positioning relative to one another. The disc 32 iskeyed to a rotatable shaft 34 so as to rotate therewith and is held inplace on the shaft by a bolt 35 and plate 36.

The shaft 34 is mounted in cantilever (FIG. 3) and rotatably supportedby bearings 37 and is driven by a sprocket 38 and chain 39 from a drivesprocket (not shown) mounted on a motor drive unit 40. This motor driveunit is a variable speed unit of conventional type with suitable controlfor varying the speed of the forming wheel 24.

The vacuum forming system for the wheel 24 comprises a vacuum pump 41which creates suction in the connecting pipe or hose 42, connected tothe manifold plate 43, shown in detail in FIGS. 9 and 10 and hereinafterreferred to. As seen in FIG. 5, the manifold plate 43 is held inintimate contact with the hub 44 of the forming wheel 24 by a spring 45interposed between the inner bearing 37 and the outer face of themanifold plate and forces the latter against the forming wheel hub 44.

The manifold plate 43 is, of course, held stationary by tube 42 whilethe hub 44 rotates with the shaft 34. As seen in FIG. 9, the manifoldplate 43 is provided with a relatively long, arcuate slot 46, one end ofwhich communicates with the suction pipe 42 as at 47. As shown in FIGS.4 and 5, each of the vacuum molds 31 on the periphery of the wheel 24 isconnected by a pipe 48 to a corresponding port 49 in the hub 44. Thus,as the hub rotates, each port 49 sequentially comes to a position on themanifold plate where the arcuate slot 46 begins to cover the port, thuscreating a vacuum within the mold cavity. As the hub and wheel continueto rotate, the slot 46 maintains the vacuum with a number of successivemolds on the wheel over a large percentage of a full revolution, andwhen the end of the slot is reached, the vacuum is cut off.

Preferably, a valve 50 leading to one end of the slot 46 is employed topermit the maintenance of a good vacuum on start-up. This valve ismaintained in closed position until sufficient vacuum has beenestablished, whereupon it is opened as initial vacuum is established inall of the molds communicating with the slot 46.

A second, shorter arcuate slot 51 is connected to an air source at 52which, in proper sequence, communicates with each mold cavity andthereby ejects the finished product from the cavity, as will appear.appear The molds 31 are identical, and a description of one will sufficefor all. As seen in FIGS. 8, each mold is provided with a suitablyshaped mold cavity 53 communicating through appropriately spaced vacuumports 54 with a vacuum chamber 55 formed in the body of the mold. Asbest seen in FIG. 6, the vacuum chamber 55 is in the form of an endlesschannel extending around the bottom wall of the mold and connectedcrosswise by a central channel 55a, thus equally distributing the vacuumcreated in the chamber. The cross channel 550 is provided with athreaded insert 56 by means of which it is operatively connected to acoupling 57 carried on the end of the respective vacuum hose 48.Preferably, the insert 56 is cast in the mold during its forming.

In order to hold and seal the thermoplastic sheet around the entireperiphery of the cavity 53 during the forming operation, a vacuum groove58 is provided in the top surface of the upper edge of the mold wall.This channel communicates with the vacuum chamber 55 by a passageway 59.This sealing operation may be effected prior to or simultaneous with theapplication of vacuum to the main mold cavity 53 by means of the vacuumpump 41 so that the vacuum groove is first evacuated and clamps theedges of the sheet completely around the cavity, holding them firmlyduring the subsequent drawing of material into the cavity itself. Thesequencing of these two steps may be accomplished in one of severalways. It is most easily accomplished by relatively restricting flow fromthe cavity while maximizing flow from the vacuum groove 58 itself. Thisprecludes the need for complicated channeling and valving. However, theclamping groove and the cavity may actually be segregated from oneanother and separately valved in sequence. It may also be noted that thevacuum groove 58 may be a continuous groove or it may comprise a seriesof suitably spaced vacuum grooves extending around the upper edge of themold 31.

As previously indicated, the maniforld plate 43 is provided with a shortarcuate slot 51 connected to an air source at 52. This slot 51communicates with each mold cavity through vacuum chamber 55 in propersequence as the hub 44 rotates relative to the manifold plate andthereby ejects the finished product from the cavity at the proper time.

The complete cycle of the forming operation is best illustrated in FIGS.1 and 2 where it will be seen that the sheet of foamed thermoplastic 22is extruded from the die 20, in the manner set forth in detail in thedescription above, and after expanding passes over the spreading yoke23, from which it is directed downwardly, and tangentially engages themold 31a across itscavity opening as the wheel 24 rotates. Here it isimmediately sealed around the edges of the cavity by the vacuum groove58. At this point, vacuum has been admitted to the arcuate slot 46 inthe manifold plate 43 which continuously applies vacuum to the moldcavities as they sequentially come into registry with the arcuate slot.By the time the mold 310 has reached the point 31b at the upper end ofthe wheel, the vacuum has been cut off from the mold cavity and airpressure is applied from slot 51 to eject the formed article from themold cavity.

The continuous web 22 with the formed articles 22b still engaged istangentially stripped from the forming wheel and guided by a pair ofspaced edge-engaging rollers 60 and a backing roller 61 to the cuttingoperation to be later described. In instances where the foamed sheet 22is relatively stiff or thick, it is preferable to employ a crimpingroller 62. This crimping roller is positioned transversely of theperiphery of the forming wheel 24 and spaced upwardly therefrom so thatit only engages the sheet 22 at the junctions of the respective flatmolds 31. This is accomplished at the top of the wheel just as thematerial leaves the mold 31b and provides a hinge point across the stripwhich precludes deformation of the articles 22b or the edges around thearticles as the web is pulled straight and tangentially from the wheel.As before indicated, some thermoplastic forms require this treatment,while others do not.

While the illustrated embodiment of the invention employs a solid shaft34, this shaft may be hollow in order that water may be brought to themold wheel through the appropriate rotary joints and then to theindividual molds whenever water cooling is required. When foamedmaterials are being produced, water cooling is not particularly usefulbecause of the poor heat transfer characteristics of low density foamsand poor conductivity of such materials to the water cooled molds.Therefore, the present invention contemplates the use of air cooling bymeans of an air blower 63 which directs air as at 64 to the lowerportion of the wheel periphery, and, if desired, it may be suitablyconducted to a point adjacent the upper portion of the wheel, as at 65.

Referring now to the cutting unit 25, shown in FIGS. 12 to 15, ahorizontally disposed cutter roll 66 is rotatably supported at oppositeends by bearings 67 carried at the upper extremities of a pair ofplunger rods 68 extending from air actuated plungers in cylinders 69.Thus, as will later appear, cutting pressure may be varied by increasingor decreasing the air pressure operating the cylinders 69. As best seenin FIGS. 12 and 14,

the cutting roll 66 is provided with two radially opposed cavities 70which are bounded by raised cutting knives 71. The cavities and cuttingknives are contoured to conform to the contours of the articles whichhave been formed in the thermoplastic sheet 22 so that as the sheetadvances between the cutting roll 66 and a backup or anvil roll 72joumalled in bearings 73, the

knives 71 sever the formed articles from the selvage with the exactprofile defined by the molds. As hereinafter explained, the rotation ofthe cutting roll 66 and the relative peripheral locations of the twosets of cutting knives are coordinated with the rotation of the formingwheel 24 so as to insure precise registry of the formed articles in theadvancing sheet 22 with the cutting knives.

The cylinders 69 are supported at their lower ends by pivotalconnections 74, whereby the entire cutter roll assembly may be swungforward for rapid change of cutter roll sizes. To facilitate thisoperation, the bearings 67 are supported for vertical sliding movementby a pair of guide rails 75 and 76, as seen in FIG. 13. The forwardguide rail 75 is shorter than the rear guide rail 76 so that when thepistons on rods 68 are drawn to the bottoms of the cylinders 69, thebearings 67 and the cutting roll 66 supported thereby can clear theguideways at the bottom of the short guideway 75 when the assembly isswung outwardly. The drive means for the cutting assembly comprises amitered gear box 77 which, as seen in FIGS. 13 and 14, is driven by theforming wheel motor 40 through a universal telescoping shaft 78. Asprocket 79, driven by the gear box 77, rotates a sprocket 80 throughsprocket chain or belt 81. The sprocket 80 is mounted at the inner endof a shaft 82, journalled in bearings 83, said shaft 82 carrying asecond sprocket 84 at its outer end which is operatively connected to asprocket 85 by a chain 86. This latter sprocket 85 drives splined shaft87 which, in turn, drives an internal shaft 88 connected to a coupling89. The coupling and internal shaft 88 may be moved in and out ofengagement with the cutter roll 66 by means of the lever 90 which isactuated by an air cylinder 91. The entire assembly just described ismounted on a bracket 92 which may be moved vertically up or down by thehandle and threaded stud 93, thereby bringing the position of thecoupling 89 into line with the center of the shaft of the cutter roll66. This permits accommodation of various sizes of cutter rolls, all ofwhich may be driven even though their vertical center line may be atdifferent positions. The chain 81 which connects sprocket 79 to sprocket80 may be kept in tension by an idler 94 (FIG. 15).

As previously pointed out, the forming unit 24 and the cutting unit 25are mounted on rollers 28 and 29 respectively, and by employing atelescoping shaft at 78, these units can be moved toward or away fromone another, depending upon the timing desired.

In order to link the forming unit 24 and the cutting unit 25 togetherand maintain the proper spacing of the two during operation through theadjustable telescoping shaft 78, adjustable means are provided toconnect the two housings of these units. As will be seen from FIGS. 2and 13, the housing 25a of the cutting unit is provided with a pair oflaterally spaced, threaded blocks 110, and, similarly, the housing 24aof the forming unit is provided with two laterally spaced, threadedblocks 11]. Extending between respective pairs of blocks are threadedshafts 112, and adjacent each of the forming unit blocks 111 theseshafts are provided with sprockets 113 over which a sprocket chain (notshown) is passed. Thus, the two threaded shafts 112 may be rotatedtogether in the same direction to maintain the selected spacingadjustment of the two units. Although not shown in the drawing, asuitable hand wheel may be provided for rotating either one or the otherof these connecting shafts and simultaneously rotating the other.

The formed articles 22a which are severed from the selvage after passingbetween the cutting roll 66 and backup roll 72 ejected down a chute 95and into stacking position in the stacking unit 26. The selvage fromwhich the articles have been severed is fed by threading fingers 96,upwardly between a stripping roll 97 and the periphery of the backuproll 72 and is conducted as seen in FIG. 1 to the granulating machine27.

To facilitate the feeding of the strip of formed articles into thecutting roll, a plate 99, associated with guide fingers 98, is providedover which the advancing strip passes. A roll 100 extends transverselyacross the plate 98 which is provided with an intermediate slot 101 toaccommodate the periphery of the roll 100. Beneath the roll 100 twowheels 102 are carried by a shaft 103 and driven by a chain 104. Thesewheels operate against the roll 100, which in turn is maintained underpressure against the wheels by cylinders 105 having piston rods 106which rotatably support the shaft of roller 100. The shaft 103 carryingthe wheels is driven by an air operated slip clutch, and torque controlis provided by varying the air pressure operating the slip clutchthrough a regulator. The surface speed of the wheels is designed to begreater than the surface speed of the cutter and backup rolls whichprovides a means for feeding the strip of formed articles by grippingthe selvage at each edge between the roller and wheels.

When the articles are discharged from between the cutting roll andbackup roll, air jets 107 (FIG. 13) may be employed to transfer thearticles down a chute 95. It has been found in practice that an air jetblown across the bottom edge of a flat article, such as a tray,decreases pressure on the underside of the tray and causes it to rapidlymake the transition from horizontal to vertical and descend down thechute into stacking position.

As previously stated, the forming and cutting units are mountedsymmetrically on rails and wheels so that they may be moved intoappropriate operating positions. The forming wheel and cutting deviceare linked together by the adjustable linkage system previouslydescribed, which permits proper cutting registration of the formedarticles in one dimension. Registration for the other dimension iscontrolled by the plate 98 and the guide fingers 99 thereon, thisassembly being movable from side to side by hand wheel 98a and adjustingshaft 98b, as seen in FIG. 12. The handle 98a turns the suitablythreaded shaft 98b which threadedly engages the plate assembly 98.

It should be pointed out that the surface speed of the cutting roll 66should be slightly faster than that of the forming wheel 24, thusproviding a uniform and constant tension at all times. Since the formingwheel is a polygon rather than a cylinder, the relationship of itsperimeter to the cutting roll must be taken into consideration. Forexample, a mold or forming wheel with eight cavities and a cutting rollwith two cavities must be run on a four-to-one ratio basis. Thisrelationship of

1. A continuous method of manufacturing articles from a thermoplasticpolymeric resin strip, comprising causing a foamable thermoplasticpolymeric resin heated to a plastic state and mixed with a blowing agentunder pressure to flow along radials of a laterally diverging diepassageway to a die orifice, continuously extruding and feeding a thin,narrow strip of said resin from said die orifice at a feed rate at leastof the order of 40 feet per minute and expanding said resin to form afoam with a low density of no more than about 3 pounds per cubic foot,continuously spreading the extrudate laterally as the extrudate is fedfrom said die orifice and while the extrudate is expanding, to preventthe formation of wrinkles, thereby to form an expanded extrudate stripof the order of 0.020 to 0.300 inch thick and a maximum of about 18inches wide, and thermoforming a series of individual articles from thespread extrudate to a depth in orthogonal planes of at least of theorder of threeeighths of an inch by utilization of the heat of extrusionas the extrudate is continuously fed from said die, said forming beingaccomplished close enough to said die, and said extrudate being fedrapidly enough to permit such forming.
 2. A method in accordance withclaim 1, wherein said forming is accomplished by a series of rotatingvacuum molds.
 3. A method in accordance with claim 2, further comprisingcontinuously withdrawing said strip from the molds after forming, andsuccessively cutting the formed articles from the strip along thebounding profiles of the articles while continuously advancing the stripand while maintaining tension in the strip between the forming andcutting thereof.
 4. A method in accordance with claim 3, furthercomprising ejecting the cut articles.
 5. A method in accordance withclaim 4, further comprising stacking the ejected articles, andconducting the strip selvage to a granulator for re-use.
 6. A method inaccordance with claim 3, wherein the vacuum forming and cutting ofsuccessive articles are coordinated to ensure accuracy in the cutarticles.
 7. A method in accordance with claim 2, further comprisingvacuum sealing the areas of said strip adjacent the boundaries of themold cavities and thereafter evacuating the mold cavities.
 8. A methodin accordance with claim 1, including transversely crimping said srip atthe junctions of successive formed articles as said strip advances, toprovide flexibility between the articles in the succeeding steps of themethod.
 9. A method in accordance with claim 1, wherein the spreading isaccomplished by stretching the extrudate over a mandrel while theextrudate is expanding.
 10. A method in accordance with claim 1, whereinthe spreading is accomplished by passing the extrudate over a mandrelspaced about 2 to 3 inches from said die, and wherein the formingcommences about 6 inches from the mandrel along the length of theextrudate.
 11. A method in accordance with claim 1, wherein said resinis extruded through a cylindrical die orifice which is curved in a planeparallel to the width of the extrudate.
 12. A method in accordance withclaim 1, wherein said blowing agent is volatile, and wherein saidspreading and forming are accomplished while said blowing agent remainsunder sufficient pressure to provide plasticity for said extrudate.